This invention relates generally to fiber optic laser catheters and, more particularly, to catheters of this kind that are adapted to selectively position the optical fiber's distal tip to facilitate the sculpting out and debulking of an obstruction or occlusion in a vessel or lumen of a living body.
Catheters of this type are particularly useful in removing obstructions or occlusions such as those associated with arteriosclerosis lesions. In such procedures, the catheter is inserted into the diseased blood vessel and moved through the vessel to a position where its distal end lies immediately adjacent to the occlusion to be removed. A laser beam, commonly generated by a pulsed excimer laser, is then directed through the fiber and emitted from its distal tip, to ablate or otherwise remove the lesion. In this particular application, the laser catheter is being used to perform angiosurgery, a procedure that is commonly referred to as laser angioplasty.
In order to produce a successful angiosurgery outcome, a sufficiently larger laser-generated lumen must be created, without inflicting any damage on the remaining tissues. Blood vessels normally range in diameter from 1–10 millimeters. Therefore, any successful laser angiosurgery must be capable of producing a relatively large lumen that is typically 70–80% of the diameter of the native healthy vessel. In order to produce a sufficiently large lumen, the fiber optic laser light guide either must have a very large light-emitting area, nearly the size of the vessel, or must use a small diameter fiber and manipulate its distal tip to various positions within the vessel so as to sculpt out a large area. The large area fiber approach makes the catheter less flexible and its use therefore may be limited to non-tortuous vessels. The large area fiber approach also has the disadvantage of requiring a large catheter introducer sheath. The small fiber approach allows the catheter to have superior flexibility, but requires a method of fiber tip position control to create a lumen larger than the fiber diameter.
In the past, catheters of the large area type have been positioned using a guide wire that extends along the vessel and through the lumen of a stenosis or partial occlusion. This has not always proven to be a satisfactory means of positioning, however, because the hole in the occlusion is not always centrally located within the vessel. Moreover, in the case of a total occlusion, the hole is entirely absent and the use of a guide wire is not possible.
Catheters of the small diameter type include various kinds of structures for controlling either the X-Y or the radial and circumferential positions of the optical fiber's distal tip. This requires both a precise positioning of the catheter relative to the vessel and a precise positioning of the fiber tip within the catheter.
Even when the catheter can be precisely positioned within the vessel, it has generally proven to be difficult to sculpt away a sufficient amount of the occlusion without at the same time mechanically or thermally damaging the vessel. Such damage can occur by the mere physical rubbing of the catheter on the vessel lining, injuring the endothelial cells, or by excessive heating of various parts of the vessel wall by the laser beam. Such physical or thermal damage can lead to a significant rate of restinosis, in which hyperplasia, the excessive growth of smooth muscle cells, within the vessel is triggered, leading in some cases to even more severe blockages than were provided by the original occlusion being removed.
It should therefore be appreciated that there is a need for a fiber optic laser catheter that can be used to more reliably and more thoroughly remove an obstruction or occlusion in a vessel of a living body, in such a fashion so as not to inflict any further injury to the vessel. The present invention fulfills this need.